The debate over abortion, a focus of incessant controversy in the Americas, is heating up north and south as the region faces the election of a new U.S. president, a ruling by the highest U.S. court and the risk of the Zika virus in dozens of nations.

Abortion plays a role in every U.S. election and this one, to choose a successor to President Barack Obama in November, is no exception.

For the Democrats, front-runner Hillary Clinton and candidate Bernie Sanders say they are firmly pro-choice, while presumptive Republican nominee Donald Trump has said he opposes abortion except in cases of rape or incest, or to save the life of the mother.

Trump has also said that if elected, he would select conservative judges who could support efforts to overturn the U.S. Supreme Court's landmark Roe v. Wade decision that made abortion legal in 1973.

The Supreme Court is currently weighing a challenge to laws in Texas which critics say place a so-called undue burden on women seeking abortions.

The restrictive laws, in place since 2013, forced the closure of more than half of the state's 42 clinics.

If the Texas laws are upheld by the nation's highest court, whose decision is expected in June, advocates say they fear a ripple effect will tighten access to abortion services nationwide.

In Texas alone, if the laws are upheld, up to 75 per cent of the state's clinics are likely to close, said Jill Adams, executive director of the Center on Reproductive Rights and Justice at the University of California, Berkeley School of Law.

"That does not mean we will see a 75 per cent decrease in the abortion rate or a corresponding 75 per cent increase in the birth rate. Far from it," she said.

"We know that resourceful people will apply creativity and ingenuity and if they are pregnant and don't want to be, they will find a way not to be," she said.

Supporters of the laws say they protect women's health. They require clinics to upgrade to hospital standards and doctors performing abortions to have formal agreements to admit patients to local hospitals.

"The court's ruling in this case will impact not only millions of women in Texas, but women seeking abortion throughout the country," said a legal brief submitted to the high court by attorneys for Planned Parenthood.

Where similar laws have taken effect, the brief said, "women seeking abortion have suffered devastating consequences."

South from the Caribbean and Mexico to Brazil, the threat of the Zika virus has raised the question of making abortion available to pregnant women who have been exposed to it.

Outbreaks of the mosquito-borne Zika virus, which has been linked to microcephaly, a condition that causes babies to be born with small heads and other birth defects, have been reported in at least 41 countries or territories, most in the Americas.

In light of the threat of Zika, the United Nations High Commissioner for Human Rights, Zeid Ra'ad Al Hussein, has called on governments to reconsider policies that restrict access to services such as contraception and abortion for pregnant women.

"Laws and policies that restrict her access to these services must be urgently reviewed," he said earlier this year.

Some countries have recommended that women delay getting pregnant, advice that "ignores the reality that many women and girls simply cannot exercise control over whether or when or under what circumstances they become pregnant," he said.

The World Health Organization (WHO) has labeled the Zika outbreak a global health emergency.

"Few countries in the outbreak zone offer universal access to sexual and family planning services," WHO said in a statement.

According to a one study, nations in Latin America and the Caribbean have the highest proportion - 56 per cent - of unintended pregnancies anywhere in the world, it said.